The fulfillment of the aggravated demands on future small-size High-Speed Direct Injection (HSDI) Diesel engines requires next to the optimization of the injection system and the combustion chamber also the generation of an optimal in-cylinder swirl charge motion.
To evaluate different port concepts for modern HSDI Diesel engines, usually quantities as the in-cylinder swirl ratio and the flow coefficient are determined, which are measured on a steady-state flow test bench. It has been shown that different valve lift strategies nominally lead to similar swirl levels. However, significant differences in combustion behavior and engine-out emissions give rise to the assumption that local differences in the in-cylinder flow structure caused by different valve lift strategies have noticeable impact.
In this study an additional criterion, the homogeneity of the swirl flow, is introduced and a new approach for a quantitative assessment of swirl flow pattern is presented.
Different valve lift strategies were investigated by transient in-cylinder CFD flow simulation, applying both the Reynolds-Averaged Navier Stokes (RANS) equations and the multi-cycle Large Eddy Simulation (LES) approach. The results obtained from the LES multi-cycle approach were averaged and compared with RANS results. An evaluation of different valve strategies using three-dimensional Particle Imaging Velocimetry in a steady-state flow configuration is also presented.